1. Technical Field
The present invention relates in general to improving the curvature of a lapping plate and, in particular, to an improved method of achieving very high crown-to-camber ratios on magnetic sliders.
2. Description of the Related Art
Magnetic recording is employed for large memory capacity requirements in high speed data processing systems. For example, in magnetic disc drive systems, data is read from and written to magnetic recording media utilizing magnetic transducers commonly referred to as magnetic heads. Typically, one or more magnetic recording discs are mounted on a spindle such that the disc can rotate to permit the magnetic head mounted on a moveable arm in position closely adjacent to the disc surface to read or write information thereon.
During operation of the disc drive system, an actuator mechanism moves the magnetic transducer to a desired radial position on the surface of the rotating disc where the head electromagnetically reads or writes data. Usually the head is integrally mounted in a carrier or support referred to as a “slider.” A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disc drive system. The slider is aerodynamically shaped to slide over moving air and therefore to maintain a uniform distance from the surface of the rotating disc thereby preventing the head from undesirably contacting the disc.
Typically, a slider is formed with essentially planar areas surrounded by recessed areas etched back from the original surface. The surface of the planar areas that glide over the disc surface during operation is known as the air bearing surface (ABS). Large numbers of sliders are fabricated from a single wafer having rows of the magnetic transducers deposited simultaneously on the wafer surface using semiconductor-type process methods. After deposition of the heads is complete, single-row bars are sliced from the wafer, each bar comprising a row of units which can be further processed into sliders having one or more magnetic transducers on their end faces. Each row bar is bonded to a fixture or tool where the bar is processed and then further diced, i.e., separated into sliders having one or more magnetic transducers on their end faces. Each row bar is bonded to a fixture or tool where the bar is processed and then further diced, i.e., separated into individual sliders each slider having at least one magnetic head terminating at the slider air bearing surface.
The slider head is typically an inductive electromagnetic device including magnetic pole pieces, which read the data from or write the data onto the recording media surface. In other applications the magnetic head may include a magneto-resistive read element for separately reading the recorded data with the inductive heads serving only to write the data. In either application, the various elements terminate on the air bearing surface and function to electromagnetically interact with the data contained on the magnetic recording disc.
In order to achieve maximum efficiency from the magnetic heads, the sensing elements must have precision dimensional relationships to each other as well as the application of the slider air bearing surface to the magnetic recording disc. Each head has a polished ABS with flatness parameters, such as crown, camber, and twist. The ABS allows the head to “fly” above the surface of its respective spinning disk. In general, small (<5 nm), positive crown and camber values are desired to achieve the desired fly height, fly height variance, take-off speed, and other aerodynamic characteristics. However, there are applications that call for very high crown values in order to reduce the stiction force between head and disk when the disk is stopped. There are also applications that require negative crown values to promote the slider to contact with the disk during read/write operations. During manufacturing, it is most critical to grind or lap these elements to very close tolerances of desired flatness in order to achieve the unimpaired functionality required of sliders.
Conventional lapping processes utilize either oscillatory or rotary motion of the workpiece across either a rotating or oscillating lapping plate to provide a random motion of the workpiece over the lapping plate and randomize plate imperfections across the head surface in the course of lapping. During the lapping process, the motion of abrasive particles carried on the surface of the lapping plate is typically along, parallel to, or across the magnetic head elements exposed at the slider ABS.
Rotating lapping plates having horizontal lapping surfaces in which abrasive particles such as diamond fragments are embedded have been used for lapping and polishing purposes in the high precision lapping of magnetic transducing heads. Generally in these lapping processes, as abrasive slurry utilizing a liquid carrier containing diamond fragments or other abrasive particles is applied to the lapping surface as the lapping plate is rotated relative to the slider or sliders maintained against the lapping surface.
Although a number of processing steps are required to manufacture heads, the ABS flatness parameters are primarily determined during the final lapping process. The final lapping process may be performed on the heads after they have been separated or segmented into individual pieces, or on rows of heads prior to the segmentation step. This process requires the head or row to be restrained while an abrasive plate of specified curvature normal to the surface is rubbed against it. As the plate abrades the surface of the head, the abrasion process causes material removal on the head ABS and, in the optimum case, will cause the ABS to conform to the contour or curvature of the plate. The final lapping process also creates and defines the proper magnetic read sensor and write element material heights needed for magnetic recording.
There are a number of factors that affect the accuracy of ABS curvature during the final lapping process. These include diamond size/morphology, lubricant chemistry, lapping surface velocity, plate material, lapping motion/path on the plate, and other lapping parameters. In addition to these parameters, it is essential that the contour of the lapping plate be tightly controlled since, in the best case, the ABS will conform to the curvature of the plate. Thus, the flatness and/or curvature of the slider ABS exhibits a strong dependency on the curvature of the lapping plate used. For a given plate, the lapping property of the plate changes every time the plate is refaced and recharged. It is known in the trade that a so-called “good plate” is key to achieve consistent and within-specification slider flatness. Likewise, it is not uncommon to see a so-called “bad plate” cause unacceptable sliders.
In the plate charging operation, the plate is covered with a layer of diamond-containing slurry. A charge ring, made of ceramic material that is harder than the plate material while softer than diamond, sits on the plate and pushes the diamond grits into the plate material as the plate and ring turn. In the early phase of the charging process, the contact surface between a charge ring and a plate is primarily determined by the charge ring contour. After a plate is fully charged with diamond grits, it starts to modify the contour of the charge ring according to the plate surface profile. It is very common to see an out-of-specification plate modify the charge ring shape such that it is no longer possible to maintain its original shape.
In the prior art, vacuum or mechanically-distorted plates can be charged with complementary contour charge rings so that even charging can be achieved on the plates. It is difficult to maintain such exacting matched plates and charges. Furthermore, the plate contour is not a conical one and exhibits second order flatness deviations on the plate, which degrade slider parametrics in addition to crown. Thus, it would be highly desirable to control the lapping property of a lapping plate after it is charged so that a desired amount of precise flatness or curvature of the plate can be predetermined.